This is still something I find myself arguing over with people now and again. How did this idea start? Why did this idea start? I guess this is a question about the history of history but maybe someone could shine some light on the topic for me.
These ideas arise from the post-bellum "Lost Cause" movement. Slavery, though one of many issues, was integral in the division between the North and South in the Civil War.
Here are some links you might find helpful:
[Is this AskReddit comment about the U.S. Civil War not being about slavery accurate?] (https://www.reddit.com/r/AskHistorians/comments/3aph04/is_this_askreddit_comment_about_the_us_civil_war/?)
How accurate is it to say that the Civil War wasn't about slavery
When did Southerner's start denying that the Civil War was bout slavery?
Is it really true that American Slavery had to expand or collapse